Derivative products

An overlay analysis is the process of overlaying 2 or more spatial layers and capturing statistics associated with their relative coverage. In this case, the sub-watershed layer is overlain by Provincial land-use and surficial geology layers to obtain information like percent impervious, relative permeability, etc.

Provincial layers discussed in more detail below have in all cases been re-sampled to the 50x50m² grid associated with the hydrologically corrected DEM. It is from these rasters where the aggregation of watershed characteristics is computed.

Land use

The Ministry of Natural Resources and Forestry (2019) SOLRIS version 3.0 provincial land use layer is employed to aggregate imperviousness and canopy coverage at the sub-watershed scale. In areas to the north, where the SOLRIS coverage discontinues, interpretation was applied by:

  1. Using Provincial mapping of roads, wetlands and water bodies, areas outside of the SOLRIS data bounds (typically up on the Canadian Shield) are filled in with the appropriate SOLRIS land use class index (201, 150, 170, respectively–MNRF, 2019); and,
  2. All remaining area not covered by SOLRIS is assumed Forest (SOLRIS land use class index of 90), as observed with satellite imagery.

The dominant SOLRIS land use class (by area) is assigned the Land use class index for every 50x50m² grid cell.

Final 50x50m SOLRIS mapping. Final 50x50m SOLRIS mapping. (For illustrative purposes only see here to reproduce shown raster.)

Land use coverage

For any ~10km² sub-watershed and give a 50x50m² grid , there should be a set of roughly 4,000 SOLRIS land use class indices. Using a look-up system, the set of cells contained within a sub-watershed are assigned a value of imperviousness, water body, wetland and canopy coverage (according to their SOLRIS index) and accumulated to a sub-watershed sum.

Percent impervious and canopy coverage as per SOLRIS v3.0 (MNRF, 2019) land use classification.
SOLRIS Land use classification
Index Name Imperviousness (%) Canopy cover (%)
11 Open Beach/Bar
21 Open Sand Dune
23 Treed Sand Dune 50
41 Open Cliff and Talus
43 Treed Cliff and Talus 50
51 Open Alvar
52 Shrub Alvar 25
53 Treed Alvar 50
64 Open Bedrock
65 Sparse Treed 40
81 Open Tallgrass Prairie 10
82 Tallgrass Savannah 35
83 Tallgrass Woodland 85
90 Forest 100
91 Coniferous Forest 100
92 Mixed Forest 100
93 Deciduous Forest 100
131 Treed Swamp 50
135 Thicket Swamp 50
140 Fen 25
150 Bog 25
160 Marsh 25
170 Open Water
191 Plantations – Tree Cultivated 85
192 Hedge Rows 85
193 Tilled
201 Transportation 85
202 Built-Up Area– Pervious 10 10
203 Built-Up Area– Impervious 90
204 Extraction–Aggregate
205 Extraction –Peat/Topsoil 10
250 Undifferentiated

Final 50x50m impervious mapping. (For illustrative purposes only see here to reproduce shown raster.)

Final 50x50m canopy mapping. Final 50x50m canopy mapping. (For illustrative purposes only see here to reproduce shown raster.)

Surficial geology

The Ontario Geological Survey’s 2010 Surficial geology of southern Ontario layer also assigns a 50x50m² grid by the dominant class.

Final 50x50m permeability mapping. Final 50x50m permeability mapping. (For illustrative purposes only see here to reproduce shown raster.)

Permeability

The OGS classes have been grouped according to the attribute “permeability” using a similar look-up table cross-referencing scheme. OGS (2010) adds: “Permeability classification is a very generalized one, based purely on characteristics of material types.”

After assigning an assumed “effective” hydraulic conductivity to every permeability group, sub-watershed “permeability” is then calculated as the geometric mean of 50x50m² grid cells contained within a sub-watershed. Effective hydraulic conductivity value assumed for every permeability group is shown here:

Permeability classifications (after OGS, 2010) and assumed effective hydraulic conductivities.
K (m/s)
Low 1e-09
Low-medium 1e-08
Medium 1e-07
Medium-high 1e-06
high 1e-05
unknown/variable 1e-08
fluvial 1e-05
organics 1e-06

The resulting effective hydraulic conductivity is then reverted back to the nearest Low–High OGS (2010) classification.

Source code

Processing discussed above that are operational have been documented in a jupyter notebook. Source data can be found here and additional outputs can be found here.

References

Ministry of Natural Resources and Forestry, 2019. Southern Ontario Land Resource Information System (SOLRIS) Version 3.0: Data Specifications. Science and Research Branch, April 2019

Ontario Geological Survey 2010. Surficial geology of southern Ontario; Ontario Geological Survey, Miscellaneous Release— Data 128 – Revised.